Serena Williams won’t be trying that again. (Dennis Grombkowski/Getty Images)

They say, “When in Rome, do as the Romans do.” That’s certainly better advice than doing as Serena Williams recently did. The tennis superstar, competing at the Italian Open, said she got very ill at her hotel — after trying some of her dog’s food.

Now, this wasn’t Purina that Williams sampled. Her hotel, which appeared to be the very posh Rome Cavalieri, offered its own room-service menu for dogs, of which Williams has been availing herself on behalf of her three-year-old Yorkshire Terrier, Chip.

In admirably candid, self-shot video clips shared via Snapchat Wednesday, Williams recounted how she had ordered Chip a perfectly tasty-sounding entree (“Beef and Chicken with Vegetables”) the day before. “I was like, ‘That looks so good,’ ” she noted. Then she went with the Salmon and Rice and thought, “That looks like the best food … it looks better than my food!”

Well, it does look like people food. Well, it does look like people food.

To bolster her claim, Williams showed the dish in question, and it did appear reasonably appetizing, in a blurry sort of way. The urge to find out if it tasted as good as it looked proved irresistible, so the world’s top-ranked women’s player went ahead and tried some.

“Don’t judge me, I ate a spoonful!” Williams exclaimed to the camera. However, “it did taste weird … a little bit like a house-cleaner thing,” and the result left more than just a bad taste in her mouth.

“I don’t think it’s consumable for humans,” Williams said. “They should have wrote that!”

Long story short, the 21-time Grand Slam event winner felt compelled to hightail it to the bathroom within a couple of hours. But Williams found a bright side to her painful predicament.

“I guess tomorrow, when I step onto the court, I’m going to look [sucking in her cheeks] … svelte,” she said.

Here is video of Williams’s snaps: